Merck & Co wanted to reduce hepatitis C treatment to just four weeks. It made an attempt to do the same by adding Gilead Sciences' drug, Sovaldi, to its oral two-drug combination. But the result was nowhere near the desired efficacy, as a high rate of relapses was reported.

Merck is not the only company, which has been trying to further reduce the treatment time, while maintaining cure rates above 90%. In the ongoing trial of earlier untreated patients, just 38.7% of them did not have any detectable signs of the liver destroying virus.